Basic Black Is Best:

Study Evaluates Influence of Colored Mulches on Commercial Strawberry Production

 David Himelrick and Randy Akridge

Many commercial strawberry growers in the Southeast grow their crops on raised beds. This hill culture method provides numerous advantages for production and relies heavily on the use of plastic mulches, which help control weeds, enhance soil temperatures, and regulate soil moisture. For many years, black plastic has been the standard mulch used in these production systems. However, many other plastic mulch color options are available to producers, each reportedly providing different production advantages. AAES research indicates that, in most cases, black plastic is still the best choice for Alabama growers.

A three-year study was conducted by AAES scientists to evaluate the effects of various colored plastic mulches on total, early, and late season yield in annual hill strawberry production systems. The study was conducted at the Brewton Experiment Field in Escambia County using seven mulch treatments the first two years and two additional mulches in the third year.

View of strawberry plastic mulch trials at the Brewton Experiment Field.

The treatments included: nonmulched bare-ground, clear plastic, black plastic, black-on-white plastic, white-on-black plastic, IRT-76, ALOR-brown, red, and silver. IRT-76 and ALOR-brown are made with infrared transmitting film, which selectively screens out light waves that would encourage weed growth while letting in light rays that will warm the soil. Chandler and Selva cultivars (varieties) were planted into the treatments. Chandler is the industry standard and Selva is a day neutral variety that may help producers lengthen their harvest season.. 

Chandler plants typically averaged more than twice the yield of the Selva plants in all treatments. Because black plastic is the standard industry practice, all treatments were viewed with this as the benchmark.

Yields on black plastic mulches differed only from the significantly reduced yields found on nonmulched, bare-ground treatments. Although not significantly different in any year, the top performing mulch treatments varied with production year and cultivar. During the first year of the study, in which the harvest season was wet and warm, the highest yielding treatments were IRT-76, clear, and ALOR-brown for Chandler cultivars and clear, black, and ALOR-brown for Selva. The following year, the harvest season was dry and cool, and the top performers were white-on-black, black, and ALOR-brown for Chandler and ALOR-brown, IRT-76, and white-on-black for Selva. During the final year of the study, which provided cool and moderately wet weather conditions, and the best performance was recorded on black, white-on-black, and clear for Chandler and black, IRT-76, and clear for Selva. Nonmulched treatments consistently produced the lowest yields.

The use of various plastics to influence soil temperature and affect the aerial microclimate around the plant to shift, accelerate, delay, or extend the harvest season was inconsistent. Generally, the plastic mulches that produced the highest soil temperatures caused plants to flower and fruit earlier. The laminated white-on-black resulted in the coolest soil temperatures of any mulch treatment and improved late-season performance in the two cool harvest season years. Average soil temperatures from warmest to coolest were found with black, black-on-white, clear, IRT-76, ALOR-brown, red, silver, white-on-black, and bare soil treatments.

After three years of research on the feasibility of using a variety of plastic mulches to maximize production and possibly extend fruiting season, these results suggest that black plastic mulch is still the best choice for commercial plantings. In addition to productivity, the inconsistent performance of other mulches and their cost, availability, and weed control factors all suggest that black plastic mulch is the most effective and efficient choice. In certain cases a white-on-black mulch, which keeps the soil cooler in hot weather, may be useful to extend the harvest season later into the spring.